Bruce Anderson used to recommend the W4CS. It is an OK plug, but Silver can't compare with Platinum for durability, and it does not have a projected tip.

Here is what we have so far. Basically, you want to stay away from copper/nickel with multi-spark and stock CDI, as the center electrode erodes away faster than platinum, and the larger diameter takes away energy from the spark gap.

I strongly prefer the projected tip, as this reduces fouling, and I think it has a better idle. You can live without it, but why?